The present invention relates to electronic devices.
It is generally recognized that conventional VLSI integrated technical technology will be prevented from further scaling by the time MOS devices get down to a quarter micron channel length, and perhaps even at much larger geometries. Since much of the advance in integrated circuit capabilities has been based on the continued progress of scaling, this near-future barrier is of substantial concern.
Thus it is an object of the present invention to provide an integrated circuit technology wherein active devices can have active regions smaller than one quarter micron in dimension.
It is further object of the present invention to provide an integrated circuit technology wherein active devices can be fabricated which occupy a total area of less than 1/4 of a square micron average for each active device.
A further inherent limitation of conventional integrated circuit technology is speed. MOS devices have inherent limits on their speed due to the channel-length transit time. Intergrable bipolar devices also have inherent speed limitations, due to the base width transit time, and are also likely to have high power dissipation.
Thus it is an object of the present invention to provide an active device having higher potential maximum speed than any MOS device.
It is a further object of the present invention to provide an active device which is potentially faster than any bipolar device.
It is a further object of the present invention to provide an active device which is potentially faster than any bipolar device, and which also has a very low power dissipation.
To achieve these and other objects, the present invention provides: a new genus of electronic devices, wherein at least two closely adjacent potential wells (e.g. islands of GaAs in an AlGaAs lattice) are made small enough that at least two components of momentum of carriers within the wells are discretely quantized. This means that, when the bias between the wells is adjusted to align energy levels of the two wells, tunneling will occur very rapidly, whereas when energy levels are not aligned, tunneling will be greatly reduced. This high-gain leads to useful electronic device functions.
A difficulty in making quantum-coupled devices into functional electronic circuits is that these devices are so extremely small that it is typically necessary to run a number of them in parallel to provide macroscopic output currents. In addition, the routing of wiring to couple into and out of these multiple parallel active devices is also difficult, since the tight geometry constraints of the devices place substantial constraints on the geometry which must be used for the wiring.
Moreover, these quantum-coupled devices have extremely low output impedence.
Thus it is an object of the present invention to provide a method for coupling the few-carrier outputs of a quantum-well device to an external signal carrying macroscopic currents.
It is a further object of the present invention to provide a method for coupling a low-impedence output from a quantum-well device to an external output with macroscopic currents.
It is a further object of the present invention to provide a method for coupling the output of multiple quantum-well devices to a single external current signal.
A further difficulty in the interface of quantum-coupled devices to the outside world is in clocking. Quantum-coupled devices have the inherent potential to be exceedingly fast, and some of the embodiments described below provide a teraHertz asynchronous logic. However, coupling such a fast unclocked logic to the outside world is obviously difficult.
A further object of the invention is to provide a static to dynamic transition, wherein the extremely fast static output of quantum-coupled-device logic could be transformed into a clocked output, at a clocked rate compatible to the outside world.
According to the present invention, to achieve the foregoing and other objects and advantages, there is provided.
An electronic device comprising:
a plurality of quantum wells, positioned and connected to embody a desired circuit function, said wells each comprising an island of a semiconducting material having a minimum dimension less than 500 Angstroms and another dimension less than 1000 Angstroms, a barrier medium being interposed between respectively adjacent ones of said wells wherein the minimum potential energy of carriers is higher than the minimum potential energy of carriers within said wells;
a metal wire having a maximum cross-sectional dimension less than 500 Angstroms;
a trapping site located less than 1500 Angstroms from one of said quantum wells and being closely electrically coupled to said metal wire; and
sensing means connected to said thin metal wire for detecting in accordance with changes in the resistance of said wire whether a carrier has been injected into said trapping site.